1. Field of the Invention
The present invention relates to a head suspension for a hard disk drive incorporated into an information or data processing apparatus such as a computer.
2. Description of the Related Art
For example, there is a conventional head suspension such as shown in FIG. 37. FIG. 37 is a plan view showing a head suspension 101 incorporated into a hard disk drive. The head suspension 101 includes a base 103, a load beam 105, and a flexure 107. The load beam 105 includes a rigid part 109 and a resilient part 111. Rails 113 are formed along the side edges in an across-the-width direction of the rigid part 109 by rising from the rigid part 109.
FIG. 38 is a partly sectioned view partly showing an example of a hard disk drive in which the head suspensions 101 are arranged. As shown in FIG. 38, the hard disk drive has a carriage 115 including arms 117. Each head suspension 101 is attached to the arm 117 of the carriage 115 via the base 103 by swaging or the like.
The carriage 115 is turned around a spindle 121 by a positioning motor 119 such as a voice coil motor or the like. By turning the carriage 115 around the spindle 121, a head 123 of the head suspension 101 is moved to a target track on a disk 125 arranged in the hard disk drive.
When the disk 125 is rotated at high speed, the head 123 slightly floats from the surface of the disk 125 against a gram load that is a load applied to the head 123 by the head suspension 101.
In recent years, application of the hard disk drives increasingly expands to a small-sized personal computer for a mobile machine or a portable (cellular) phone so that the hard disk drives are used under more severe conditions. Importance of measures to shock applied or input to the hard disk drive gradually increases.
The head suspension has a shock property that determines a lift of the slider from the surface of the hard disk when a shock is applied or input. The shock property of the head suspension is dependent on the weight of the load beam.
For example, a first head suspension has a load beam having a thickness (t) of 51 μm, a length (lL) of 7 mm, and a gram load of 2.5 gf that is applied by the load beam to a head, and a second head suspension has a load beam having a thickness (t) of 30 μm, a length (lL) of 5.5 mm, and a gram load of 2.5 gf. If a shock of 1 msec duration (1 msec in half wavelength) is applied to these head suspensions, a slider of the first head suspension lifts at an acceleration of 628 G and a slider of the second head suspension lifts at an acceleration of 1103 G.
It is understood from these examples that, to improve the shock property of a head suspension, a load beam of the head suspension must be thin and short and must have a large gram load.
Therefore, measures such as reduction of the thickness of a load beam are adopted in a head suspension for a miniaturized hard disk drive such as a 2.5-inch hard disk drive whose shock property is required to be improved.
However, a head suspension having a thin load beam sways or flutters due to air disturbance as external influence at a first torsion frequency, i.e., a resonant frequency in a first torsion mode. The sway or flutter of the head suspension at the first torsion mode is hereinafter referred to as “T1 windage” and the first torsion frequency is hereinafter is referred to as “T1 frequency.” The “T1 windage” is also indicative of the property of the sway or flutter of the head suspension. The T1 windage results in limit in improvement of positioning accuracy of the head suspension to a track.
On the other hand, the number of tracks per one inch tends to be gradually increased due to increase of a recording density of a hard disk. As this result, a track pitch becomes narrow and an allowable range of a positional deviation of the head to a track becomes further narrow. Therefore, further improvement of the positioning accuracy of the head suspension is required. The positional deviation of the head is hereinafter referred to as “off-track.”
In this way, improvements of the shock property and the T1 windage are in a trade-off relationship, but simultaneous pursuit of the both is a factor in the miniaturization of the hard disk drive.
At present, the off-track of the head is controlled by suppressing frequency with a control system. However, the control system suppresses the frequency in a range of about 0.8 to 1.3 kHz only. Therefore, the frequency excepting the range due to air disturbance can not be suppressed securely. A property of the control system almost depends on a main torsion mode of a carriage of a head suspension. Resonant frequencies in the main torsion mode are about 5 kHz in a 3.5-inch hard disk drive and about 6 kHz in a 2.5-inch hard disk drive. Accordingly, when the head suspension has T1 frequency and sway frequency which are lower than the resonant frequencies in the main torsion mode, stability of the control system may be adversely affected.
A resonant frequency in a first bending mode of the head suspension may affect stability of the control system related to the main mode of the carriage or the like. The resonant frequency in the first bending mode is hereinafter referred to as “B1 frequency.” Further, when the B1 frequency is low, the shock property also degrades. For the details of the above-mentioned related arts, Japanese Unexamined Patent Application Publication No. 09-282624 and U.S. Pat. No. 6,765,759B2.